Method for fabricating a semiconductor structure having a stable crystalline interface with silicon

ABSTRACT

A method for fabricating a semiconductor structure comprises the steps of providing a silicon substrate ( 10 ) having a surface ( 12 ); forming on the surface of the silicon substrate an interface ( 14 ) comprising a single atomic layer of silicon, nitrogen, and a metal; and forming one or more layers of a single crystal oxide ( 26 ) on the interface. The interface comprises an atomic layer of silicon, nitrogen, and a metal in the form MSiN 2 , where M is a metal. In a second embodiment, the interface comprises an atomic layer of silicon, a metal, and a mixture of nitrogen and oxygen in the form MSi[N 1− O x ] 2 , where M is a metal and X is 0≦X&lt;1.

FIELD OF THE INVENTION

The present invention relates in general to a method for fabricating asemiconductor structure including a crystalline alkaline earth metalsilicon nitrogen based interface between a silicon substrate and oxidesor nitrides, and more particularly to a method for fabricating aninterface including an atomic layer of an alkaline earth metal, silicon,and nitrogen.

BACKGROUND OF THE INVENTION

An ordered and stable silicon (Si) surface is most desirable forsubsequent epitaxial growth of single crystal thin films on silicon fornumerous device applications, e.g., ferroelectrics or high dielectricconstant oxides for non-volatile high density memory and logic devices.It is pivotal to establish an ordered transition layer on the Sisurface, especially for subsequent growth of single crystal oxides,e.g., perovskites.

Some reported growth of these oxides, such as BaO and BaTiO₃ on Si(100)was based on a BaSi₂ (cubic) template by depositing one fourth monolayerof Ba on Si(100) using reactive epitaxy at temperatures greater than850° C. See for example: R. McKee et al., Appl. Phys. Lett. 59(7), pp782-784 (Aug. 12, 1991); R. McKee et al., Appl. Phys. Lett. 63(20), pp.2818-2820 (Nov. 15, 1993); R. McKee et al., Mat. Res. Soc. Symp. Proc.,Vol. 21, pp. 131-135 (1991); R. A. McKee, F. J. Walker and M. F.Chisholm, “Crystalline Oxides on Silicon: The First Five Monolayers”,Phys. Rev. Lett. 81(14), 3014-7 (Oct. 5, 1998). U.S. Pat. No. 5,225,031,issued Jul. 6, 1993, entitled “Process for Depositing an OxideEpitaxially onto a Silicon Substrate and Structures Prepared with theProcess”; and U.S. Pat. No. 5,482,003, issued Jan. 9, 1996, entitled“Process for Depositing Epitaxial Alkaline Earth Oxide onto a Substrateand Structures Prepared with the Process”. However, atomic levelsimulation of this proposed structure indicates that it likely is notstable at elevated temperatures.

Growth of SrTiO₃ on silicon (100) using an SrO buffer layer has beenaccomplished. T. Tambo et al., Jpn. J. Appl. Phys., Vol. 37 (1998), pp.4454-4459. However, the SrO buffer layer was thick (100 Å), therebylimiting application for transistor films, and crystallinity was notmaintained throughout the growth.

Furthermore, SrTiO₃ has been grown on silicon using thick metal oxidebuffer layers (60-120 Å) of Sr or Ti. B. K. Moon et al., Jpn. J. Appl.Phys., Vol. 33 (1994), pp. 1472-1477. These thick buffer layers wouldlimit the application for transistors.

Therefore, a method for fabricating a thin, stable crystalline interfacewith silicon is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 illustrate a cross-sectional view of a clean semiconductorsubstrate having an interface formed thereon in accordance with thepresent invention;

FIGS. 3-6 illustrate a cross-sectional view of a semiconductor substratehaving an interface formed from a silicon nitride layer in accordancewith the present invention; and

FIGS. 7-8 illustrate a cross-sectional view of an alkaline-earth-metalnitride layer formed on the structures illustrated in FIGS. 1-6 inaccordance with the present invention.

FIGS. 9-12 illustrate a cross-sectional view of a perovskite formed onthe structures of FIGS. 1-8 in accordance with the present invention.

FIG. 13 illustrates a side view of the atomic structure of oneembodiment of the layers of FIG. 12 in accordance with the presentinvention.

FIG. 14 illustrates a top view along view line AA of FIG. 13 of theinterface.

FIG. 15 illustrates a top view along view line AA of FIG. 13 includingthe interface and the adjacent atomic layer of the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To form the novel interface between a silicon (Si) substrate and one ormore layers of a single crystal oxide or nitride, various approaches maybe used. Several examples will be provided for both starting with a Sisubstrate having a clean surface, and a Si substrate having siliconnitride (Si₃N₄ or the like) on the surface. Si₃N₄ is amorphous ratherthan single crystalline and it is desirable for purposes of growingadditional single crystal material on the substrate that a singlecrystal nitride be provided as the interface.

Turning now to the drawings in which like elements are designated withlike numbers throughout, FIGS. 1 and 2 illustrate a semiconductorstructure including a Si substrate 10 having a clean surface 12. A clean(2×1) surface 12 may be obtained with any conventional cleaningprocedure, for example, with thermal desorption of SiO₂ at a temperaturegreater than or equal to 850° C., or by removal of the hydrogen from ahydrogen terminated Si(1×1) surface at a temperature greater than orequal to 300° C. in an ultra high vacuum. Hydrogen termination is a wellknown process in which hydrogen is loosely bonded to dangling bonds ofthe silicon atoms at surface 12 to complete the crystalline structure.The interface 14 of a crystalline material may be formed by supplying(as shown by the arrows in FIG. 1) controlled amounts of a metal, Si,and activated nitrogen, either simultaneously or sequentially to thesurface 12 at a temperature less than or equal to 900° C in a growthchamber with N₂ partial pressure less than or equal to 1×10⁻⁶ mBar. Themetal applied to the surface 12 to form the interface 14 may be anymetal, but in the preferred embodiment comprises analkaline-earth-metal, such as barium (Ba) or strontium (Sr).

As the application of the Ba, Si, and activated nitrogen form BaSiN₂ asthe interface 14, the growth is monitored using Reflection High EnergyElectron Diffraction (RHEED) techniques which are well documented in theart and which can be used in situ, i.e., while performing the exposingstep within the growth chamber. The RHEED techniques are used to detector sense surface crystalline structures and in the present processchange rapidly to strong and sharp streaks by the forming of an atomiclayer of the BaSiN₂. It will of course be understood that once aspecific manufacturing process is provided and followed, it may not benecessary to perform the RHEED techniques on every substrate.

The novel atomic structure of the interface 14 will be described insubsequent paragraphs.

It should be understood by those skilled in the art that thetemperatures and pressures given for these processes are recommended forthe particular embodiment described, but the invention is not limited toa particular temperature or pressure range.

Alternatively, in forming the interface 14, oxygen may be supplied alongwith the metal, silicon, and nitrogen to form a mixture. The ratio ofnitrogen to oxygen may vary substantially, but preferably would beapproximately 80%.

Referring to FIGS. 3-6, another approach comprises forming a Sisubstrate 10 having a surface 12, and a layer 16 of silicon nitridethereupon. The layer 16 of silicon nitride can be formed purposely in acontrolled fashion known in the art, e.g., by applying (arrows) activenitrogen onto the surface 12. The silicon nitride layer can also beformed on Si substrate using both silicon and active nitrogen in anultra high vacuum. See for example, R. Droopad, et. al., U.S. Pat. No.5,907,792, issued May 25, 1999, entitled “Method of Forming a SiliconNitride Layer”. The novel interface 14 may be formed at least in one ofthe two suggested embodiments as follows: By applying analkaline-earth-metal to the surface 18 of silicon nitride layer 16 at700-900° C., under an ultra high vacuum. More specifically, the Sisubstrate 10 and the amorphous silicon nitride layer 16 are heated to atemperature below the sublimation temperature of the silicon nitridelayer 16. This can be accomplished in a molecular beam epitaxy chamberor Si substrate 10 can be at least partially heated in a preparationchamber after which it can be transferred to the growth chamber and theheating completed. Once the Si substrate 10 is properly heated and thepressure in the growth chamber has been reduced appropriately, thesurface 12 of the Si substrate 10 having silicon nitride layer 16thereon is exposed to a beam of metal, preferrably analkaline-earth-metal, as illustrated in FIG. 5. In a preferredembodiment, the beam is Ba or Sr which is generated by resistivelyheating effusion cells or from e-beam evaporation sources. In a specificexample, Si substrate 10 and silicon nitride layer 16 are exposed to abeam of Ba. The Ba joins the silicon nitride and converts the siliconnitride layer 16 into the interface 14 comprising BaSiN₂ in acrystalline form. Alternatively, an alkaline-earth-metal may be providedto the surface 18 at lower temperatures, annealing the result at700-1000° C., in an ultra high vacuum. In another embodiment, oxygen maybe supplied with the nitrogen to form the interface 14, resulting in acrystalline form of BaSi[N_(1−x)O_(x)]₂.

Once the interface 14 is formed, one or more layers of a single crystaloxide, nitride, or combination thereof, may be formed on the surface ofthe interface 14. However, an optional layer of an alkaline-earth-metaloxide, such as BaO or SrO, may be placed between the interface 14 andthe single crystal oxide. This alkaline-earth-metal oxide provides a lowdielectric constant (advantageous for certain uses such as memory cells)and also prevents oxygen from migrating from the single crystal oxide tothe Si substrate 10.

Referring to FIGS. 7 and 8, the formation of alkaline-earth-metalnitride layer 22 may be accomplished by either the simultaneous oralternating supply to the surface 20 of the interface 14 of analkaline-earth-metal and active nitrogen at less than or equal to 700°C. and under N₂ partial pressure less than or equal to 1×10⁻⁵ mBar. Thisalkaline-earth-metal nitride layer 22 may, for example, comprise athickness of 50-500 Å.

Referring to FIGS. 9-12, a single crystal oxide layer 26, such as analkaline-earth-metal perovskite, may be formed on either the surface 20of the interface 14 or the surface 24 of the alkaline-earth-metalnitride layer 22 by either the simultaneous or alternating supply of analkaline-earth-metal oxide, oxygen, and a transition metal, such astitanium, at less than or equal to 700° C. under an oxygen partialpressure less than or equal to 1×10⁻⁵ mBar. This single crystal oxidelayer 26 may, for example, comprise a thickness of 50-1000 Å and will besubstantially lattice matched with the underlying interface 14 oralkaline-earth-metal oxide layer 22. It should be understood that thesingle crystal oxide layer 26 may comprises one or more layers in otherembodiments.

Referring to FIG. 13, a side view (looking in the <10> direction) of theatomic configuration of the Si substrate 10, interface 14, andalkaline-earth-metal metal oxygen layer 26 is shown. The configurationshown comprises, in relative sizes, for illustrative purposes, fromlarger to smaller, strontium atoms 30, silicon atoms 32, nitrogen atoms34, and titanium atoms 36. The Si substrate 10 comprises only siliconatoms 32. The interface 14 comprises metal atoms (which in the preferredembodiment are illustrated as strontium atoms 30), silicon atoms 32, andnitrogen atoms 34. The alkaline-earth-metal nitrogen layer 26 comprisesstrontium atoms 30, nitrogen (or a combination of nitrogen and oxygen)atoms 34, and titanium atoms 36.

Referring to FIG. 14, a top view of the interface along view line AA ofFIG. 13, shows the arrangement of the strontium, silicon, and nitrogenatoms 30, 32, 34.

Referring to FIG. 15, a top view along line AA of FIG. 13, shows theinterface 14 and the top atomic layer 11 of the Si substrate 10.

For this discussion, a monolayer equals 6.8×10¹⁴ atoms/cm² and an atomiclayer is one atom thick. It is seen that the interface 14 shown in theFIGs. comprises a single atomic layer, but could be more than one atomiclayer, while the Si substrate 10 and the alkaline-earth-metal metalnitrogen layer may be many atomic layers. Note that in FIG. 13, onlyfour atomic layers of the Si substrate 10 and only two atomic layers ofthe alkaline-earth-metal metal nitride layer 26 are shown. The interface14 comprises a half monolayer of the alkaline-earth-metal, a halfmonolayer of silicon, and a monolayer of nitrogen. Each strontium atom30 is substantially equally spaced from four of the silicon atoms 32 inthe Si substrate 10. The silicon atoms 32 in the interface 14 aresubstantially on a line and equally spaced between thealkaline-earth-metal atoms in the <110> direction. Each silicon atom 32in the top layer of atoms in the Si substrate 10 is bonded to a nitrogenatom 34 in the interface 14 and each silicon atom 32 in the interface 14is bonded to two nitrogen atoms 34 in the interface 14. The three-foldbonding coordination of the nitrogen atoms at the interface 14 issatisfied in this interface structure, which greatly lowers the totalenergy of the interface layer 14, thus enhancing its stability. Theinterface 14 comprises rows of strontium, silicon, and nitrogen atoms30, 32, 34 in a 2×1 configuration on a (001) surface of the Si substrate10, 1× in the <10> direction and 2× in the <110> direction. Theinterface 14 has a 2×1 reconstruction.

A method for fabricating a thin, crystalline interface 14 with silicon10 has been described herein. The interface 14 may comprise a singleatomic layer. Better transistor applications are achieved by theinterface 14 being thin, in that the electrical coupling of theoverlying oxide layers to the Si substrate 10 is not compromised, and inthat the interface 14 is more stable since the atoms will more likelymaintain their crystalinity in processing. This alkaline earthmetal-Si-nitrogen-based interface also acts as a diffusion barrier tooxygen and other elements.

What is claimed is:
 1. A method of fabricating a semiconductor structurecomprising the steps of: providing a silicon substrate having a surface;forming on the surface of the silicon substrate an interface comprisinga single atomic layer of silicon, nitrogen or a mixture of nitrogen andoxygen, and a metal; and forming one or more layers of a single crystalmaterial on the interface.
 2. The method of fabricating a semiconductorstructure of claim 1 wherein the interface comprises a single atomiclayer of silicon, nitrogen, oxygen, and a metal.
 3. The method offabricating a semiconductor structure of claim 1 wherein the materialcomprises one of a nitride, an oxide, and a mixture of a nitride and anoxide.
 4. The method of fabricating a semiconductor structure of claim 1wherein the forming the interface step includes forming a 2×1reconstruction.
 5. The method of fabricating a semiconductor structureof claim 1 wherein the forming the interface step includes forming asurface with a 2×1 reconstruction.
 6. The method of fabricating asemiconductor structure of claim 1 wherein the forming an interface stepincludes forming the interface in an ultra-high-vacuum system.
 7. Themethod of fabricating a semiconductor structure of claim 1 wherein theforming an interface step includes forming the interface in a chemicalvapor deposition system.
 8. The method of fabricating a semiconductorstructure of claim 1 wherein the forming an interface step includesforming the interface in a physical vapor deposition system.
 9. Themethod of fabricating a semiconductor structure of claim 1 wherein theforming an interface step comprises forming a single atomic layercomprises silicon, nitrogen, oxygen, and an alkaline-earth-metal. 10.The method of fabricating a semiconductor structure of claim 1 whereinforming an interface step comprises the steps of: forming a half of amonolayer of an alkaline-earth-metal; forming a half of a monolayer ofsilicon; and forming a monolayer of nitrogen.
 11. The method offabricating a semiconductor structure of claim 1 wherein the forming aninterface step comprises the step of forming one or more monolayers of amixture of oxygen and nitrogen.
 12. The method of fabricating asemiconductor structure of claim 1 wherein the single crystal materialcomprises oxides, nitrides, or a mixture of oxides and nitrides.
 13. Themethod of fabricating a semiconductor structure of claim 1 wherein thesingle crystal material comprises one or more layers of oxides,nitrides, or a mixture of oxides and nitrides.
 14. The method offabricating a semiconductor structure of claim 1 wherein the singlecrystal material comprises alkaline-earth-metal oxides.
 15. The methodof fabricating a semiconductor structure of claim 1 wherein the singlecrystal material comprises perovskites.
 16. The method of fabricating asemiconductor structure of claim 1 wherein the forming an interface stepcomprises forming a single atomic layer comprises silicon, nitrogen, andan alkaline-earth-metal.
 17. The method of fabricating a semiconductorstructure of claim 16 wherein the alkaline-earth-metal is selected fromthe group of barium and strontium.
 18. A method of fabricating asemiconductor structure comprising the steps of: providing a siliconsubstrate having a surface; forming one of silicon nitride, siliconoxide, or a mixture of oxide and nitride on the surface of the siliconsubstrate; providing an alkaline-earth-metal on the silicon nitride,silicon oxide, or a mixture of oxide and nitride; and heating thesemiconductor structure to form an interface comprising a single atomiclayer adjacent the surface of the silicon substrate.
 19. The method offabricating a semiconductor structure of claim 18 wherein the heatingstep includes forming the interface with a 2×1 reconstruction.
 20. Themethod of fabricating a semiconductor structure of claim 18 wherein thesteps of providing an alkaline-earth-metal and heating the semiconductorstructure are accomplished in an ultra-high-vacuum system.
 21. Themethod of fabricating a semiconductor structure of claim 18 wherein thesteps of providing an alkaline-earth-metal and heating the semiconductorstructure are accomplished in a chemical vapor deposition system. 22.The method of fabricating a semiconductor structure of claim 18 whereinthe steps of providing an alkaline-earth-metal and heating thesemiconductor structure are accomplished in a physical vapor depositionsystem.
 23. The method of fabricating a semiconductor structure of claim18 wherein the heating step includes forming an interface having asingle atomic layer of silicon, nitrogen, oxygen, and analkaline-earth-metal.
 24. The method of fabricating a semiconductorstructure of claim 18 wherein heating step includes forming an interfacestep comprises the steps of: forming a half of a monolayer of analkaline-earth-metal; forming a half of a monolayer of silicon; andforming a monolayer of nitrogen.
 25. The method of fabricating asemiconductor structure of claim 18 wherein heating step includesforming an interface step comprises the steps of: forming a half of amonolayer of an alkaline-earth-metal; forming a half of a monolayer ofsilicon; and forming a monolayer of nitrogen and oxygen.
 26. The methodof fabricating a semiconductor structure of claim 18 wherein heatingstep includes forming one or more monolayers of a mixture of oxygen andnitrogen.
 27. The method of fabricating a semiconductor structure ofclaim 18 wherein the heating step includes forming an interface having asingle atomic layer of silicon, nitrogen, and an alkaline-earth-metal.28. The method of fabricating a semiconductor structure of claim 27wherein the alkaline-earth-metal is selected from the group of bariumand strontium.
 29. A method of fabricating a semiconductor structurecomprising the steps of: providing a silicon substrate having a surface;providing an alkaline-earth-metal on the surface of the siliconsubstrate; and providing silicon and nitrogen to form an interfacecomprising a single atomic interface with the surface of the siliconsubstrate.
 30. The method of fabricating a semiconductor structure ofclaim 29 the step of providing silicon and nitrogen to form an interfacealso includes providing oxygen.
 31. The method of fabricating asemiconductor structure of claim 29 wherein the steps of providing analkaline-earth-metal and providing silicon and nitrogen are accomplishedin an ultra-high-vacuum system.
 32. The method of fabricating asemiconductor structure of claim 29 wherein the steps of providing analkaline-earth-metal and providing silicon and nitrogen are accomplishedin a chemical vapor deposition system.
 33. The method of fabricating asemiconductor structure of claim 29 wherein the steps of providing analkaline-earth-metal and providing silicon and nitrogen are accomplishedin a physical vapor deposition system.
 34. The method of fabricating asemiconductor structure of claim 29 wherein the providing silicon andnitrogen step comprises the steps of: forming a half of a monolayer ofan alkaline-earth-metal; forming a half of a monolayer of silicon; andforming a monolayer of nitrogen.
 35. The method of fabricating asemiconductor structure of claim 29 wherein the forming an interfacestep comprises the step of forming one or more monolayers of a mixtureof oxygen and nitrogen.
 36. The method of fabricating a semiconductorstructure of claim 29 wherein the providing silicon and nitrogen stepcomprises forming a single atomic layer of silicon, nitrogen, and analkaline-earth-metal.
 37. The method of fabricating a semiconductorstructure of claim 36 wherein the alkaline-earth-metal is selected fromthe group of barium and strontium.
 38. The method of fabricating asemiconductor structure of claim 29 wherein the providing silicon andnitrogen step comprises forming an interface having a 2×1reconstruction.
 39. The method of fabricating a semiconductor structureof claim 30 wherein the providing silicon and nitrogen step comprisesthe steps of: forming a half of a monolayer of an alkaline-earth-metal;forming a half of a monolayer of silicon; and forming a monolayer ofnitrogen and oxygen.
 40. The method of fabricating a semiconductorstructure of claim 8 wherein the heating step includes forming a surfacewith a 2×1 reconstruction.